The present disclosure relates to the field of data processing, and more specifically to gray component replacement in color conversions.
Digital devices that create (e.g., scanners and digital cameras), display (e.g. CRT and LCD monitors), or print (e.g. ink-jet and laser printers) colors typically define color data using color spaces. Generally, a color space is a combination of a color model and a gamut. A color model defines each color within the model using primary components, such as, in the case of a Red, Green, Blue (RGB) color model, the levels of red, green, and blue light components needed to create each color, or in the case of a Cyan, Magenta, Yellow, and Key (CMYK) color model, the levels of cyan, magenta, yellow, and black ink needed to create each color. Some color models use primary components that are not primary colors, but are more abstract, such as the CIE XYZ color space. Levels of each component in the color models typically range from 0 to 100 percent of full intensity, which may be represented on a scale of 0 to 1. By varying the levels or intensities of the primary components, various colors in the color model may be created. However, as a practical matter a device is often limited in its ability to produce pure cyan, magenta, or yellow ink, which limits its range of colors or color gamut. A gamut is simply the range of colors that may be displayed on, rendered by, or captured by a particular device.
Each device, depending on its limitations and definitions for pure primary colors, may have a different color gamut and color spaces. To facilitate rendering the same color in two different color spaces such that the color appears substantially the same in both color spaces, conversion methods may be performed. Converting from one device-dependent color space to another is often accomplished through an intermediary device-independent color space, which define colors in more absolute terms. Some examples of device-independent color spaces include the CIE XYZ. CIE L*a*b* (luminance, a, b), and CIE LCH (luminance, chroma, hue) color spaces. The relationship of a device's native color space with a device-independent color space typically is described by some combination of formulas, transfer functions, matrices, and look up tables. This relationship may be stored in an International Color Consortium (ICC) profile for the device. Methods to convert among the various device-independent color spaces are well known in the art.